Method and apparatus for surfacing sheet material



May 17, 1960 c, c ET AL METHOD AND APPARATUS FOR SURFACING SHEET MATERIAL Filed Nov. 27, 1957 4 Sheets-Sheet 1 s M m N 54 7 W2 4 mm? 5 a 5 w May 17, 1960 D. c. RICH ETAL METHOD AND APPARATUS FOR SURFACING SHEET MATERIAL Filed NOV. 27, 1957 4 Sheets-Sheet 2 w Bl V/ $215 52 BY 65047653.

May 17, 1960 D. c. RICH ETAI- METHOD AND APPARATUS FOR SURFACING SHEET MATERIAL Filed Nov. 27, 1957 Fig. 6

4 Sheets-Sheet 3 INVESTOR-5 aw/o c. 2/0 JAMES (F. 4*?67/5? BY 6502652 #442445 May 17, 1960 D. c. RICH ETAL METHOD AND APPARATUS FOR Filed NOV. 27, 1957 4 Sheets-Sheet 4 m m an E HEB vmme meew 4 I a 0:0 W w JV.

ATT'OlC/VE'Y United States Patent 2,936,551 METHOD AND APPARATUS FOR SURFACING SHEET MATERIAL David C. Rich and James E. Archer, Pittsburgh, Pa, and George R. Harrison, Belmont, Mass, assignors to Pittsburgh Plate Glass Company, Allegheny County, Pa.,

a corporation of Pennsylvania 7 Application November 27, 1957, Serial No. 699,281 17 Claims, c1. 51-140 This application relates to method and apparatus for polishing plate glass, and specifically concerns polishing discrete sheets or a continuous ribbon of plate glass in order to smooth the ma or surfaces by removing surface irregularities uniformly across its entire width.

The general aim of the present invention is to provide a novel method and apparatus for polishing glass in which a polishing composition is rubbed on the glass with a simple continuous motion cross-wise of the sheet. The advantages which inhere, and the principles of operation will become apparent as the description of an exemplary installation proceeds, taken in connection with the accompanying drawings in which:

a Figure 1 is an end elevational View of a polishing section of a line for continuously surfacing a ribbon of material constructed according to the principles of the present invention.

Figure 2 is a schematic disclosed in Figure 1.

Figure 3 is a plan view of an alternate embodiment of apparatus disclosed in Figures 1 and 2.

Figure 4 is a plan view of a single station of the apparatus disclosed in Figures 1 and 2.

Figure 5 is a part sectional, part elevational view taken along the lines VV of Figure 4.

Figure 6 is a section taken through the head shaft assembly of Figure 5.

Figure 7 is an enlarged detailed sectional view taken through a portion of the polishing belts and ribbon shown in Figure 5.

Figure 8-is an enlargeddetailed sectional view of a portion of an upper pressure shoe shown in Figure 5.

Figure 9 is a detailed longitudinal elevation, partly in section, of a portion of the polishing section shown in Figures land 2. 1

.Figure 10 is.a partial perspective view showing the tus.

The apparatus disclosed comprises a conveyor C extending horizontally through one or more polishing stations P. Each polishing station includes a frame F,

which comprises an upper cross bridge structure and a lower cross bridge structure 16 interconnected by sup port pillars 17, that flank the conveyor C. The upper cross bridge structure 15 crosses the conveyor along a plane spaced above the path of movement of the ribbon, whereas the lower bridge structure 16 crosses the con,-

veyor C along a plane spaced below the path of movement for the ribbon. Theupper cross bridge structure includes H-beams 18 and 19 that extend longitudinally of the conveyor C.

The conveyor C comprises spaced conveyor rolls 20. for supporting a glass ribbon for movement along the conveyor C, with pinch rolls 22 located beyond the polishing station P to drive the glass ribbon forwardly plan view of the apparatus structural relationship ofcertain elements of the apparadrive sprocket 30 and a driven. sprocket 34 to drive the latter. The roller chain 32 is of a quadruple width type 10 and the gear teeth of the drive sprocket 30 and the driven sprocket 34 are so chosen as to provide a 2 to 1 reduction.

The driven sprocket 34 is keyed to a driven sprocket shaft 36, otherwise known as the upper belt head shaft, A pair of head by means of a gib key 38 (Figure 6).

l5 shaft sheaves 40 are keyed by means of continuous keys 42 to the upper belt head shaft 36. The sheaves 40 are apertured at aligned apertures 44 to receive a bolt 46' which is externally threaded at its extremities 48 to receive nuts 50. The sheaves 40 are separated by an apertured spacer 52, whose apertures 53 are aligned with the sheave apertures 44. When the nuts 50 on the threaded endsof thebolts 46 are moved toward each other, the sheaves are. held as a solid unit. While solid sheaves are preferred, the width of the belt used is such that it has been foundto, be economical to utilize sheaves that are available commercially and to bolt them together in the manner disclosed.

Each sheave 40 comprises a peripheral flange 54 secured about the periphery of the bolted sheave by means of bolts 56. The frame F carries pillow blocks 57 (Figure 6) for sup-porting the upper belt head shaft 36 and additional pillow blocks which support an upper tail shaft 58 (Figure 5). Tail shaft sheaves 60, which correspond in structure to the head shaft sheaves 40, are keyed to the head shaft sheaves to the upper belt head shaft. 36.

A pair of parallel polishing belts 62 run between the head shaft sheaves 40, and the tail shaft sheaves 60.

Each polishing belt 62 comprises a sheave facing layer.

order of 28 inches). The polishing felts may be white 70, on the order of 4; inch wide and A2 inch deep, which intersectgrooves 69 to facilitate distribution of polishing composition. As shown in Figures 7 and 10, the polishing belt is ribbed and grooved at its sheave facing surface to provide a series of alternate ribs 72 and grooves 74 which engage similarly arranged ribs and grooves of the upper sheaves 40 and 60.

The upper belt drive motor 24 is rotated in a clockwise direction as seen in Figure 5 to cause the upper belt head shaft 36 to rotate the head shaft sheaves 40 in a clockwise direction and cause the upper polishing belt to sweep acrossthe upper surface of the moving ribbon from right to left as seen in the drawing. The direction of the belt travel is such that the tension side of the belt is,

presented to the glass.

tail shaft 58 in a manner similar to the keying of the.

68 mounted in strips 2 inches wide extending. across the entire width of the polishing belt (on the which carry free running shafts 82 to which are mounted upper backup rolls 84, which are flanged at 85. A backup belt 86 is entrained between upper backup rolls 84 and comprises a backup roll facing portion 88 of a fluorocarbon product noted for its low friction properties, such as Rulon B, manufactured by the Dixon Corporation of Bristol, Rhode Island, and a polishing belt facing portion 89. The outer surface of the backup belt 86 (portion 89) comprises alternate ribs 90 and grooves 92 which mesh with the ribs 72 and grooves 74 of the polishing belt 62.

In the present instance, a pressure shoe is employed for pressing a flat run of the belt flight against the glass surface to be polished with substantially uniform pressure per unit area throughout the entire area of contact of the belt run and the glass sheet.

The lower run of the low friction facing 88 contacts and slides against the bottom surface of an upper pressure shoe 94, which surface may be faced with a lacquer composition containing small graphite particles, such as a composition called Electrofilm supplied by Electrofilm, Inc., North Hollywood, California. The flanges 85 at the extremities of the backup rolls 84 guide the movement of the upper backup belt 86. The free running shafts 82 for the backup pulleys 84 are adjustable in position in their respective plilar blocks so that the angle of incidence of the polishing felt with the edge of the glass ribbon and the pulley tension can be regulated. The backup belt 86 is driven by engagement of its ribs 90 and grooves 92 with the grooves 74 and ribs 72, respectively, of the polishing belt 62. V

A lower polishing belt 100 is driven by the lower belt drive motor 26 through alower drive shaft 102, lower drive sprocket 1G4, lower roller chain 106, lower driven sprocket 188, lower belt head shaft 110, and lower drive sheaves 112. The lower polishing belt 100 is built identically to the upper polishing belt 62 and is entrained around lower drive shaft sheave '112 and lower tail shaft sheave 114.

The assembly also includes a lower backup belt 116 which is built similarly to the upper backup belt 86 and is entrained upon free running lower backup pulleys 118. The upper run of lower backup belt 116 moves over the upper surface of a lower pressure shoe 120, which is faced in a manner similar to upper pressure shoe 94. Motor 26, like motor 24, rotates in a clockwise direction in order to have the tension side of the lower polishing belt 100 presented to the glass surface.

.The glass ribbon shown generally by G in Figures 7 and 9 is wiped from right to left at its upper surface and from left to right at its lower surface. The opposite movements applied to the opposite glass surfaces minimize any tendency to veer the ribbon that would tend to occur if the opposing felts were both moved in the same transverse direction in rubbing contact across the ribbon.

The lower pressure shoe 120 provides a bottom support plane for the lower backup belt 116 (Figure 8). The shoe 120 is bolted to flanges 122, each forming part of a guide shaft 124. A pair of the latter is mounted for vertical'sliding movement in ball bushing housings 126,'which are carried by the lower bridge 16 of frame F below 7 A rotatable driving shaft 128 is mounted on a bearing housing 13%) carried by the frame F. Miter gears 132 fixed to the shaft 128 mesh with miter gears 134 keyed to cam drive shafts 136 which extend horizontally at right angles to the driving shaft 128. A pair of eccentric cams 138 are keyed to each cam drive shaft 136. Each cam drive shaft 136 is free to rotate 180 degrees to exert a, vertical lifting force on the lower pressure shoe 120. The weight of the lower pressure shoe causes it to rest directly on the upper peripheral surfaces of the cams 138. 'Rotation of the shaft 128 results in raising or lowering the lower pressure shoe 120. This verthe bottom surface of the lower pressure shoe tical adjustment is provided to adjust the compression on the sponge rubber backing of the lower polishing belt and also allow the ribbon to be surfaced to enter a polishing station without causing tilting from the plane defined by pinch rolls 22.

The upper pressure shoe 94 is connected to a pressure shoe support plate 142. The latter in turn is apertured to receive a vertical guide shaft 144 at each corner. Each aperture is countersunk to receive a vertical guide shaft flange 146 (Fig. 8). A rigid washer 148 secures the flange 146 in place in the countersunk portion. Each vertical guide shaft 144 is slidable vertically in axially aligned ball bushings 150 carried by bushing housings, which, in turn, are supported by the support frame F, and keyed to a sleeve 152. A pressure shoe bridge 154 interconnects the sleeves 152..

The shafts 144 help support a box 162. The latter is open at its top and is provided with a floor 164 and walls 166 so that it can carry weights. Weights may be added or removed as desired in order to adjust the pressure of the upper pressure shoe 94- against the upper polishing belt 62. This pressure is supplied by the mass of the box 162 and its supported weights bearing upon the upper pressure shoe 94 through the vertical guide shafts An air cylinder 170 is located to the side of the apparatus. This cylinder is pivotally connected at its bottom end to the lower bridge 16 and slidably supports a piston therein. A piston rod 171 is fixed at its lower end to the piston and at its upper end to a lifting beam 172. The lifting beam 172 is pivoted about a fulcrum 174 supported on a brace 176 carried by the H-beam 18 of upper bridge 15. A roller bearing 178 ismounted on a bearing rod 180 carried by a bifurcated end 182 of the lifting beam 172.

Vertical motion of the air cylinder piston rod 171 causes the lifting beam 172 to rotate about its fulcrum 174, thus moderating the pressure supplied to the back of the polishing belt 62 through the weights included in the Weight box 162. Thus, the weights provide adjust to H beam 19 of upper bridge 15. An adjustable bolt 186 is screw threaded through the bearing bracket 184 to bear against the upper surface of the lifting beam 172 and limit the downward movement of the upper pressure shoe 94 toward the upper ribbon surface.

Each corner of the upper pressure shoe 94 is pro.

vided with an upper inclined surface 188 in the region below the axis of movement of the vertical guide shaft 144, as shown in detail in Figure 8. A wedge 190 is slidably mounted on the upper inclined surface 188. The wedge is displaceable laterally by means of an adjustment screw 192 which is screw threaded through'a threaded housing 194 fixed to the pressure shoe 94. A locking nut 196 fixes the location of the wedge transversely of the axis of movement of the vertical guide shaft 144.

.After establishing which is the lowest corner of the pressure shoe 9.4, the remaining corners of the shoe can be adjusted to the same horizontal plane by adjusting the t adjustment screws 192 at the other three corners of the pressure shoe 94 until all four corners are in horizontal alignment. Then, the corners are locked into position by tightening the locking nuts 196 against the threaded housings 194. The upper surface of the wedge 190 is wedged between the bottom spherical surface 191 of the vertical guide shaft 144 and the upper inclined surface 188 of the pressure. shoe 94 to effect such adjustment.

At each station provision is made for introducing polishing slurry to the, polishing belt v Suitable compositions for this purpose are disclosed in application Serial assess-1 No. 773,411, filed November 12, 1958, of Albert Junge and assigned to the assignee of the present invention. The Junge application refers to the present application at page 24. In the present instance each polisher station is provided with a feed pipe 202 for the upper polishing belt, each'extencling longitudinally along one side of the apparatus slightly outboard of the upper tail shaft and between the upper ail shaft and lower head shaft. The feed pipe 202 includes a series of fan spray nozzles 204directed .upwardly to apply a polishing composition such as a slurry or fluid to the bottom surface of the upper polishing belt 62 and the grooves 69 sep arating its felt strips 68. The feed pipe 202 is supported to the frame F by means of supports 206.

, At the other side of the polishing station another feed pipe 208 for the, lower polishing belt 160 is located. Feed pipe 298 extends longitudinally of the conveyonC slightly outboard of the upper belt drive sheave' illand lower tail sheave 114. Feed pipe 208 includes a series of nozzles each directed obliquely downwardly and in: wardly toward the upper run oflower polishing belt 100 to dispense polishing fluid onto the upper surface of the lower polishing belt 1% and. the grooves separating the felt strips before the latter contact the lower surface of the: ribbon. frame F. Feed pipes 202 and 2il8 are connected to a supply tank of polishing slurry where theslurry is agitated in order to render it suitable for immediate use, ply tank is fed periodically from a storage tank (not shown).

Spent or unused polishing composition is permitted to drop below the conveyor C and into a recessed portion Supports 212 support feed pipe 208 to the 214 and eventually into a drain 216 where the spent pol-- ishing solution may be recovered and rejuvenated before pumping it back to the storage tank. The detaiis of the recovery system'and the storage system do not form part of the present invention but their operation has been generally described in order to provide a better understanding of the present invention.

1 Beyond each polishing station P is a flushing assembly 220 comprising a housing enclosing pinch rolls 22 and conveyor rolls 20. On either side of the pinch rolls 22, an -upper flushing pipe 222 extends transversely above, and a lower flushing .pipe 224 extends transversely below the support level of the glass sheet provided by the conveyor C. Each upper and lower flushing pipe is horizontally aligned in a vertical plane beyond an upper squeegee 226 and lower squeegee 228 which wipe the polishing composition from the ribbon surfaces. Water is flushed through the pipes to spray, on the upper and lowersurfaces of the ribbon after the latter passes beyond the Squeegees 226 and 228. Additional upper sq'ueegees23il and lower squeegees 232 wipe the flushing water from the surfaces of the glass ribbon. Each assernbly of squeegees and flushing pipes is mounted within a container 234 for receiving spent flushing water. A drain pipe (not shown) removes water from the con tainer to a sewer.

The typical construction of a polishing line, shown schematically in Figures 1 and 2, is quite suitable for using fast acting chemical compositions for polishing ground plate glass simultaneously on both surfaces. In this operation, a maximum of two polishing stations is ordinarily sufficient iQSlHOOll'l the surfaces of a continuous glass ribbon, previously ground smooth-using laterally moving felts in cooperation with polishing slurries that react rapidly with glass to form masking compositions. Thus, because certain chemical compositions used to assist in the rapid polishing of glass may cause a slight film to form, a post polishing station comprising a pairof opposed conventional spider type polisher runners R is provided to remove the slight chemical stain with the assistance of rougep The post polishing station employing a rouge slurry The sup:

l. e can be an additional beltpolisher station P instead of a post polishing station R employing a spider type runner. In the latter event, it is desirable to have 'four polishing stations P, a first station for polishing utilizing fast act ing chemicals, a second station for a stand-by chemical polishing station, a third station for post polishing utilizing rouge and a fourth station used as a stand-by for the third station. p

In Figure 3, a construction of a polishing line is shown in which the belts are disposed to rub the opposing major surfaces of the glass obliquely to the path of glass ribbon movement.

The operation of typical apparatus such as has just been described involves the entry of a ground ribbon of glass into a polishing station P. The ribbon or sheet is pulled forward by the rotation of the pinch rolls 22 with its upper surface rubbed by the polishing slurry impregnated felts 63 of the upper belt 62 which are moving. from right to left as seen in Figure 5, while simultaneously, the bottom surface of the ribbon is being rubbed by the polishing composition impregnated felts of the upper run of the lower belt 160 which are simultaneously moving from left to right. Polishing compositiontis fed to the lower run of the upper belt 62 through nozzles 204 of pipe 202 before the lower run touches the glass, while the pipe 208 feeds polishing solution through the fan type nozzles 21b to the upper run of the lower belt before the lower belt contacts the lower surface of the ribbon G. Sufl'lcient surfacing agent is fed to insure that a film is continuously maintained between. the ribbon and the felts traveling across the latter.

. Various modifications can be made in the above apparatus without departing from the spirit of the present invention. For example, the size and number of belts employed may be changed to conform with the require-; ments of distribution necessitated by the chemicalemz, ployed. Also, the ribs and grooves of the interengaging surfacesof the polishing belt and backup belt maybe dispensed with if the belts are maintained under-sulficient tension to insure the desired control of movement; Otherstructural details may be modified provided the apparatus performs the function desired according to the present inventive concept.

Both surfaces of glass sheets conveyed through a single polishing station were polished simultaneously using' apolishing composition containing'5 parts by weight anhydrous hydrofluoric acid (HF), 45 parts by weight potassium bifluoride (KFHF), parts by weight sugar; (C H O and 100 parts by weight of water. Chromium oxide (Cr O was added to the above composition to provide 4 tion. In Table A, the kw. load tabulated is the power recorded to run the motors driving the pulleys carrying upper and lower polishing belts, each equipped with 76 felt pads A x 2" x 28", which were glued to the belt at distances of separation of 4; inch from each other. The zero reading for kw. load necessary to drivethe polishing belts in the absence of any rubbingaction, which varied between about tabulated data.

inthefollowing tests, glass sheets 3i inches wide were conveyed through a single twin belt polishing station at a speed of inches per minute for one or more passes as indicated in the accompanying table. In these tests, the felts made rubbing contact with 28 inches of width across the glass surfaces. The glass sheets were at a room temperature of about 75 F. before each pass.

A Test I was run to demonstrate the effect of belt speed percent of the weight of the composi- 4 to 6, is included in the.

stant conditions of belt speed and polishing composition feed rates.

TABLE A.

Test I KW load Ave.

temp. Number V of glass of Belt speed Feed rate Pressure coming passes (it./min.) (gaL/rnin.) (p.s.i.) Top Bottom out from given under plate belt, F.

Test II Test III Test IV Approx.

TABLE B Parts by weight Ingredient Rouge CF20: slurry' slurry Water. 1, 000 1, 000 Rouge (Binney and Smith superfine-0.6 mu

1 average particle size) 500 Copperas 50 156 ClzOa (average particle sizeuuder 1 run)... v 631 Both series of tests produced polished surfaces having a commercially acceptable finish. The best results as determined by visual inspection were produced in a glass sheet subjected to treatments described in Example I.

' Example I v A sheet of twin ground plate glass about 34% inches wide by 218 inches long and of a nominal thickness of 14 inch was mounted on a conveyor and passed through abelt polishing station such as described above at a linear speed of 150 inches per minute. The belts were moved to rub opposite surfaces of the twin ground sheet at a speed of 1,000 feet per minute. The pressure shoes were adjusted to provide a pressure'ofo p.s.i. The

polishing composition utilized contained Sparts by weight anhydrous HF, 45 parts by weight KFHF, parts by Weight sugar (C' H O and 100 parts by weightof water. Five percent by weight of chromium oxide (Cr O was added tothe above composition to'produce an abrasive slurry. The slurry was applied to the polishing belts rubbing the two surfaces at a total rate of approximately 1.5 gallons per minute.

The plate was conveyed between upper and lower polishing belts to polish an area approximately 160 inches long by 28 inches wide at the center of the sheet. After passing between the oppositely moving polishing belts, the plate was passed between squeegees to remove the polishing composition and then flooded with tap' water and squeegeed again. After the tap water was squeegeed from the surfaces of the glass sheet, the sheet was conveyed to the loading end of the polishing station and then the polishing operation was repeated until the plate was subjected to three passes. 7

After the third pass, a piece of glass 8 feet long by 34% inches wide taken from the center of the length of the sheet was post polished using a rouge copperas composition by means of a polishing spider having three freely rotatable polishing runners mounted on vertical axes forming an equilateral triangle about the center of rotation of the spider. This post polishing was performed one surface at a time by translating the 8 foot length of each surface under the polishing spider. The feed rate of rouge slurry and the pressure of the spider against the surface undergoing post polishing were made as similar as possible to the conditions present at the finishing end of a conventional rouge polishing line. After the post polishing was completed, a two foot wide sample was cut from the center of the 34% inch wide sheet and one surface was silvered. The definition of images in the mirror formed was acceptable.

The machine described above employed more than one ton of force in applying a pressure of 3 p.s.i. over an area 28 inches wide and 28 inches long in the direction of glass travel. The back-up belts serve to insure that optimum efiiciency of the motors results by minimizing sliding friction at the belt-pressure shoe interfaces and minimizing slippage at the polishing belt-back-up belt interface, thus convert-ing as much of the power output of the driving motors as possible into a rubbing force at the polishing belt-glass surface interfaces. The back-up belts of the present apparatus must be capable of withstanding the heat associated with the high loading forces imposed on the glass through the pressure shoes without impairing the low friction coefiicient between the back-upbelts and the pressure shoes and also of avoiding excessively rapid wear on the part of the polishing belt.

Apparatus according to the present invention is designed to polish plate glass on a continuous basis 24 hours a day. The description of a particular embodiment of the present invention has been for illustration rather than limitation. Reference to the latter maybe obtained from the accompanying claims.

What is claimed is:

l. A method of polishing a sheet of plate glass comprising moving the sheet endwise along a horizontal.

5. The method according to claim 4, wherein the mo tion app-lied to the polishing composition rubbing one surface opposes the motion applied to the polishing composition rubbing the opposite surface.

6. The improvement in the art of polishing plate glass which comprises continuing the longitudinal motion of an uncut ribbon of plate glass as it emerges from a twin grinding operation and subjecting the moving ribbon to the rubbing action of a polishingcomposition carried by an opposed pair of sets of polishing pads moving transversely in a non-rotary direction of the path of ribbon movement in pressurized contact with substantially the entire width of opposing surfaces of the ribbon.

7. In the method of surfacing a rigid sheet of glass moving along an axis of movement, the improvement comprising moving surfacing means in pressurized contact with opposite surfaces of the sheet in opposing unidirectional non-rotary paths intersecting said axis.

8. An apparatus for rubbing the surface of a sheet of plate glass with a polishing composition, said apparatus comprising, in combination, means for advancing the sheet endwise at a continuous speed in a single direction in a horizontal plane, an endless belt resiliently deformable with respect to its thickness dimension and arranged with a flat run thereof extending transversely across the sheet, power means for driving said belt at a linear speed which is several times the speed of advance of the sheet, and means for pressing said flat run of the belt against the sheet surface to be polished with substantially uniform pressure per unit area throughout the entire area of contact of said run and sheet.

9. An apparatus for simultaneously rubbing the opposite surfaces of a sheet of plate glass with a polishing composition, said apparatus comprising, in combination, means for advancing the sheet endwise at a continuous speed in a single direction in a horizontal plane, an endless belt resiliently deformable with respect to its thickness dimension and arranged with a fiat run thereof extending transversely across each surface of the sheet, power means for driving each belt at a linear speed which is several times the speed of advance of the sheet, and means for pressing said flat run of each belt against the opposite sheet surfaces to 'be polished with substantially uniform pressure per unit area throughout the entire area of contact of said run and sheet 10. Apparatus as in claim 9, wherein the power means are so constructed and arranged as to drive said fiat runs of the belts in opposite directions 11. Apparatus as in claim 9, including polishing composition dispensing means for conveying polishing composition to the interface between each flat run and a glass surface.

12. Apparatus for surfacing a ribbon of plate glass comprising a longitudinally extending conveyor for transporting the glass ribbon along a horizontal plane, a polishing station comprising an upper cross bridge structure extending across and above the conveyor, a lower cross bridge structure extending across and below the conveyor, an upper polishing belt entrained about pulleys supported by the upper cross bridge structure, a lower polishing belt entrained about pulleys supported by'the lower cross bridge structure, said polishing belts having polishing pads secured to their outer sides and so constructed and arranged relative to said conveyor that the lower run of the upper polishing belt and the upper run of the lower polishing belt come into contact with the opposite surfaces of said ribbon, an upper belt drive motor coupled to said upper polishing belt for moving the latter transversely of the conveyor so that its lower run moves in one direction transversely of the longitudinal axis of the'conveyor, a lower belt drive motor coupled to said lower polishing belt for driving the latter so that its upper run moves transversely of the longitudinal axis of the conveyor in a direction opposite that of the movement of the lower run of said upper polishing belt, a pressure shoe adapted for movement into pressurized contact with each said belt, and means interconnecting the pressure shoe to one of said cross bridges to provide relative movement between said pressure shoes to adjust the pressure between the opposing runs of said belts and their adjacent ribbon surfaces, and means for supplying a surfacing agent to the interface between each said belt and the adjacent ribbon surface.

13. Apparatus as in claim 12, including a flushing chamber located beyond said polishing station across said conveyor.

14. Apparatus as in claim 12, wherein the flushing chamber includes a pair of pinch rolls located beyond the polishing station in the path of conveyor movement, and means for rotating said pinch rolls in directions driving the glass along said conveyor.

15. Apparatus as in claim 12 further including a backup belt interposed between each polishing belt and a pressure shoe.

16. Apparatus as in claim 15, wherein the surface of each backup belt facing the pressure shoe comprises a film of a low friction fluorocarbon.

17. Apparatus as in claim 16, wherein each backup belt and its adjacent polishing belt comprise interengaging lugs and grooves at their facing surfaces.

References Cited in the file of this patent UNITED STATES PATENTS 339,095 Guhl Mar. 30, 1886 699,368 Clemons May 6, 1902 792,825 Harman et a1. June 20, 1905 829,191 Yarnell Aug. 21, 1906 909,544 Carney Jan. 12, 1909 1,022,827 Cox Apr. 9, 1912 1,043,194 Blevney Nov. 5, 1912 1,698,365 Hitchcock Jan. 8, 1929 1,724,703 Fox Aug. 13, 1929 1,961,441 Gipe et al June 5, 1934 2,279,782 Fowles Apr. 14, 1942 2,304,974 Waldron Dec. 15, 1942 2,330,208 Fay Sept. 28, 1943 2,581,270 McVey Ian. 1, 1952 2,772,522 Minami Dec. 4, 1956 UNITED STATES PATENT OFFICE CERT TFTCATIQN 0F CORRECTION Patent No. 2 9556551 May 17, 1960 David C., Rich et alo It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 3 line 25, for "plilar" read pillar column 5 line 8, for "ail" read tail column 10, line 55, list of references cited under "UNITED STATES PATENTS, for "Fowles" read Fowler "q Signed and sealed this 2nd day of May 19610 (SEAL) Attest:

ERNEST Wo SWIDER DAVID 1Lc LADD Attesting Ufficer Commissioner of Patents 

